1. Field of the Invention
This invention relates generally to waveguides and, more particularly, to waveguide filters.
2. Description of the Related Art
Electromagnetic signals with wavelengths in the millimeter range are typically guided to a destination by a waveguide because of insertion loss considerations. An example of one such waveguide can be found in U.S. Pat. Nos. 6,603,357 and 6,628,242 which disclose waveguides with electromagnetic crystal (EMXT) surfaces. The EMXT surfaces allow for the transmission of high frequency signals with near uniform power density across the waveguide cross-section. More information on EMXT surfaces can be found in U.S. Pat. Nos. 6,262,495 and 6,483,480.
In some waveguide systems, filters are used to control the flow of signals during transmission and reception. The filters are chosen to provide low insertion loss in the selected frequency bands and high power transmission with little or no distortion. A band-stop filter can be used to block undesired signals from reaching the receiver or from being transmitted. The filter can be tuned to a different resonant frequency using mechanical adjustments such as tuning screws as disclosed in U.S. Pat. No. 5,471,164 or movable dielectric inserts as disclosed in U.S. Pat. No. 4,124,830. The screw and insert can be mechanically adjusted to change the length of a resonant cavity in the filter. The tuning occurs because the resonant frequency of the filter changes when the length is varied. Mechanical tuning, however, is slow and inaccurate because it is usually done manually. If the mechanical adjustment cannot tune the resonant frequency quickly enough, then the filter will not effectively block signals with frequencies that vary as a function of time.